This invention relates to disposable diapers and incontinent pads. More particularly, it relates to disposable diapers which are characterized in their content of an agent which inhibits ammonia formation caused by the decomposition of urine.
It is known that ammonia dermatitis or "diaper rash" is caused or is potentiated by free ammonia generated in a urine-wet diaper in contact with an infant's skin. The ammonia is formed by bacterial enzymatic decomposition of urinary urea by a wide variety of fecal bacteria such as Bacterium ammoniagenes, a saprophytic gram positive bacillus, and Proteus vulgaris, a gram negative bacillus. In view of this knowledge, the art has proceeded along essentially two lines in the prevention of diaper rash. In one approach, the prior art has attempted to prevent the liberation of ammonia from urine-wet diapers by means of chemical agents which trap the gaseous ammonia generated by the ammonia producing bacteria. Such ammonia immobilizing agents include inter alia weak organic and inorganic acids such as acetic, citric, and boric acid, capable of forming ammonium salts. The ammonia immobilizing agent may be impregnated throughout the absorptive wadding or located in discrete gas permeable sachets enfolded within the diaper.
Another approach to the prevention of diaper rash has been to incorporate a bacteriostatic agent in the diaper structure. Various carboxylic acids have been used for this purpose. U.S. Pat. No. 3,707,148 issued to Bryce on Dec. 26, 1972, for example, describes the use of carboxylic acids to inhibit microbial growth and ammonia formation. This patent discloses disposable diaper structures impregnated with citric, malic, maleic, malonic, succinic, tartaric, and fumaric acids. It has now been discovered that several of the specified carboxylic acids, citric acid for example, dissolve too rapidly when the diaper is wetted with urine, such that the urine as it wicks out to the edge of the diaper is relatively concentrated in acid, and the center of the diaper loses its protection against ammonia formation. As a result, skin irritation can occur at the diaper margins due to the excessively low pH at this point. Other carboxylic acids, e.g., fumaric acid, while dissolving more slowly relative to wicking rate, still produce excessively low pH at the edge of the diaper because they are relatively strong acids and there are no basic ions for buffering due to ion exchange of the urine as it wicks through the diaper.
Thus, a suitable acid for use in the present context must have a slow dissolution rate relative to the wicking time and should be a relatively weak acid to the end that it is capable of maintaining a pH level throughout the diaper that is compatible with the babies' skin pH and effective at inhibiting ammonia generation.